Infrared vision devices have the ability to view heat sources, such as people, in complete darkness. However, these devices are unable to differentiate words, symbols and other “regular” signs. In order to convey such information, it should be a temperature difference between objects in order to achieve sufficient discrimination.
There is a common method to create images for thermal devices by using different emissivity materials, such as used in passive thermal targets, when a low emissivity base material (usually lower than 0.4 emissivity) is used and a high emissivity material (higher than 0.7 emissivity) is printed or attached to it. The low emissivity material is intended to reflect sky energy, which its temperature on a clear day can drop to 30 Celsius degrees below zero, towards the vision device and appears “cold”, while the high emissivity material has the surrounding temperature and appears warmer. This method is limited to outdoor use and sky conditions, moreover the positioning angle is very critical in order to reflect correctly.
In other methods a heated targets is used that requires power source or using a chemical reaction for this purpose.
There are other known methods that are disclosed in some publications;
U.S. Pat. No. 3,986,384 to Giorgi—“Variable Contrast Passive Infrared Target”
U.S. Pat. No. 4,058,734 to Vroombout—“Passive Infrared Resolution Target”
U.S. Pat. No. 4,549,814 to Creel et al.—“Test Plate Having A Thermal Test Pattern”
U.S. Pat. No. 6,806,480 to Reshef—“Multi-Spectral Products”, also published by the WIPO under WO 02/03006.
These methods have advantages, drawbacks and limitations. Therefore, the present invention provides a new method that overcame the disadvantages of the mentioned methods and provides a method and a label for recognizing figure or figures by infrared vision devices in any environment.